Bacteria of the Streptococcus genus have been implicated as causal agents of disease in humans and animals. The Streptococci have been divided into immunological groups based upon the presence of specific carbohydrate antigens on their cell surfaces. At present, groups A through O are recognized (Davis, B. D. et al., In: Microbiology, 3rd. Edition, page 609, (Harper & Row, 1980). Streptococci are among the most common and important bacteria causing human disease. Although Streptococci of the B group are associated with animal disease (such as mastitis in cattle), Streptococcus agalactiae (a group B Streptococci) has emerged as the most common cause of human neonatal sepsis in the United States and is thought to be responsible for over 6000 deaths annually (Hill, H. R. et al., Sexually Transmitted Diseases, McGraw Hill, pp. 397-407). Group B Streptococcus is also an important patbogen in late-onset meningitis in infants, in postpartum endometritis, and in infections in immunocompromised adults (Patterson, M. J. et al., Bact. Rev. 40:774-792 (1976)). Although the organism is sensitive to antibiotics, the high attack rate and rapid onset of sepsis in neonates and meningitis in infants results in both high morbidity (50%) and mortality (20%) (Baker, C. J. et al., New Eng. J. Med. (Editorial) 314(26):1702-1704 (1986); Baker, C. J. et al., J. Infect. Dis. 136:137-152 (1977)).
Group B Streptococcus is a common component of normal human vaginal and colonic flora. While the most common route of neonatal infection is intrapartum from vaginal colonization, nosocomial spread in newborn nurseries has also been described (Patterson, M. J. et al., Bact. Rev. 40:774-792 (1976)). However, only a small percentage of infants colonized with group B Streptococcus develop serious infections. The role of both host factors and bacterial virulence determinants in the transition from colonization to infection is not well understood.
Several proteins from group B Streptococcus are thought to have a role in virulence and immunity (Ferrieri, P, Rev. Infect. Dis. 10:S363 (1988)). In 1975, Lancefield defined the C proteins of group B Streptococcus by their ability to elicit protective immunity (Lancefield, R. C, et al., J. Exp. Med. 142:165-179 (1975)). This group of proteins is thought to contain several different polypeptides and antigenic determinants. In view of these findings, efforts to prevent infections with group B Streptococcus have been directed towards the use of prophylactic antibiotics and the development of a vaccine against group B Streptococcus (Baker, C. J, et al., Rev. of Infec. Dis. 7:458-467 (1985), Baker, C. J. et al., New Eng. J. Med. (Editorial) 314(26): 1702-1704 (1986)). Polysaccharide vaccines against group B Streptococcus are described by Kasper, D. L. (U.S. Pat. No. 4,207,414 and U.S. Reissue Patent RE31672, and U.S. Pat. Nos. 4,324,887, 4,356,263, 4,367,221, 4,367,222, and 4,367,223), by Carlo, D. J. (U.S. Pat. No. 4,413,057, European Patent Publication 38,265), and by Yavordios, D. et al. (European Patent Publication 71,515), all of which references are incorporated herein by reference.
Except for the small sub-population of infants in whom both maternal colonization with group B Streptococcus and other perinatal risk factors can be identified, the use of prophylactic antibiotics has not been practical or efficacious in preventing the majority of cases (Boyer, K. M, et al., New Eng. J. Med. 314(26):1665-1669 (1986)). lntrapartum chemoprophylaxis has not gained wide acceptance for the following reasons: (1) It has not been possible to identify maternal colonization by group B Streptococcus in a fast, reliable and cost-effective manner; (2) About 40% of neonatal cases occur in low-risk settings; (3) It has not been considered practical to screen and/or treat all mothers or infants who are potentially at risk; and (4) antibiotic prophylaxis has not appeared to be feasible in preventing late-onset meningitis (7200 cases per year in the United States) or postpartum endometritis (45,000 cases annually) (Baker, C. J. et al., New Eng. J. Med. (Editorial) 314:1702-1704 (1986)).